The constant demand for shrinking device sizes by the semiconductor industry requires continuous improvement in resolving power in state-of-the-art lithography tools. For example, immersion lithography has arisen as an effective enhancement technique to extend the resolution limits of optical lithography, and is expected to enable manufacturing of highly integrated circuits at the 45 nm node in 2008. Resolution requirements at the 32 nm node will require even more advanced lithographic solutions due to smaller device dimensions compared to previous nodes. One of the potential techniques to overcome the optical resolution limit of 193 nm scanners at the 32 nm node is “double exposure,” where the total aerial image is sub-divided into two independent exposure passes having relaxed spatial resolution requirements. These two images are added sequentially to achieve the desired final pattern geometry. Such approach encompasses doubling the number of all photomasks used for “double exposure'” as well as doubling processing time, tool time and materials usage, resulting in increased cost. If adopted, this particular technology solution is expected to be applied to multiple levels resulting in a significant increase in cost of ownership (COO). Therefore, methods that can compensate this potentially elevated COO such as more efficient wafer processing (reduced cycle times, reduction in the total number of processing steps, reduction in volume of raw materials used) would partially compensate for the aforementioned higher manufacturing costs associated with future lithographic nodes.
One additional requirement for patterning schemes targeted at advanced lithographic nodes is the need to sustain resolution, CD control and etch selectivity. One way to achieve this comprises multiple pattern transfers into highly etch selective films, such as in a trilayer patterning scheme (S. Burns et al., “Trilayer Development for 193 nm Immersion Lithography,” J. Photopolymer Sci. Tech., 2007, Vol. 20, No. 5, p. 679). One example of a trilayer system involves coating a thick planarizing underlayer followed by the application of separate etch-resistant (e.g. spin-on silicon-containing Bottom Anti-Reflective Coating or BARC) and imaging (resist) layers. When the BARC typically is a partially or completely opaque material, it has the imaginary part of complex refractive index, k, above about 0.1. The typical k photoresist, on the other hand, is usually below about 0.1 (the imaginary part of complex refractive index, k) which we define as partially or completely transparent. In some instances, the imaginary part of complex refractive index, k can comprise about 0.1 for the BARC or the photoresist. In any event in one embodiment of the invention, the BARC typically is partially or completely opaque and the photoresist is partially or completely transparent. Some of the critical advantages of trilayer lithography include large etch selectivity with the underlying substrate, the ability to use conventional chemically amplified resists, good planarization of the wafer topology, and good reflectivity control of the stack (M. Slezak et al., Semiconductor International, Feb. 1, 2007). One of the disadvantages of using a trilayer stack is the longer processing time and increased number of processing steps, which results in a more complex integration path.
At the same time, patterning arbitrary structures using projection-reduction optical systems requires the incorporation of reflectivity control techniques to decrease the unwanted reflection of DUV radiation (DUV comprising light having wavelengths of 193 nm or 248 nm) at the top and bottom surfaces of the imaging layer.
Reflection of light from the substrate/resist interface produces variations in the light intensity and scattering in the resist during exposure, resulting in non-uniform photoresist line width upon development. Light can scatter from the interface into regions of the resist where exposure was not intended, resulting in line width variations. The amount of scattering and reflection will typically vary from region to region resulting in line width non-uniformity.
To eliminate the effects of chromatic aberration in exposure equipment lenses, monochromatic or quasi-monochromatic light are commonly used in resist projection techniques. Unfortunately, due to resist/substrate interface reflections, constructive and destructive interference is particularly significant when monochromatic or quasi-monochromatic light is used for photoresist exposure. In such cases the reflected light interferes with the incident light to form standing waves within the resist. In the case of highly reflective substrate regions, the problem is exacerbated since large amplitude standing waves create thin layers of underexposed resist at the wave minima. If the resist thickness is non-uniform, the problem becomes more severe, resulting in variable line width control.
Top anti-reflective coat (TARC) materials can prevent the multiple interference of light that takes place within the photoresist layer during exposure. However, a TARC does not reduce the notching problem that comes from the presence of topography under the photoresist layer. Instead, a BARC formed beneath the photoresist layer is capable of eliminating both swing and notching problems, and has emerged as the most effective reflectivity solution while interfering the least with the lithographic process.
Therefore, methods that can reduce the increasing number of processing steps without sacrificing the number of layers utilized in the imaging stack that are present for good reflectivity control and image transfer are required to reduce cycle time and volume of chemical used in semiconductor fabs.
In addition to the above problems associated with the critical lithography levels (levels requiring the highest imaging resolution) there are many levels that do not require high resolution imaging but cannot use the standard imaging stack comprised of resist on BARC. One such example is that of implant levels where dry-etch (plasma) transfer of the resist image into the substrate (or BARC) is not possible due to plasma damage and contamination of the substrate. Therefore imaging also becomes challenging due to poor reflectivity control.
The related art describes various methods, compositions, processes and articles of manufacture in the field of devices produced by photolithographic means. For example, Brodsky et al. United States Patent Publication No. 20080008955 describe a graded spin-on organic antireflective coating for photolithography comprising at least two polymer components in a single formulation that substantially segregate between a first substrate interface and a second photoresist interface.
Allen et al. United States Patent Publication No. 20070254237 describe a topcoat material and use thereof in immersion lithography processes.
Angelopoulos et al. United States Patent Publication No. 20070196748 describe a process of making a semiconductor device using multiple antireflective materials.
Angelopoulos et al. United States Patent Publication No. 20070015082 describe a process of making a lithographic structure using antireflective materials.
Babich et al. United States Patent Publication No. 20070015083 describe an antireflective composition and process of making a lithographic structure.
Allen et al. United States Patent Publication No. 20060188804 describe immersion topcoat materials with improved performance for application on top of a photoresist.
Allen et al. United States Patent Publication No. 20070254235 describe a self-topcoating resist for photolithography comprising a resist additive which is a compound comprising a polymer in a resist composition comprising a photoresist polymer, a photoacid generator and a solvent. The additive rises to the surface of the resist composition thereby inhibiting the leaching of unwanted material into an immersion fluid used with the composition in immersion lithography conditions.
Huang et al. United States Patent Publication No. 20060134546 describe low refractive index polymers as an underlayer for silicon-containing photoresists that exhibit high etch resistance and improved optical properties.
Baldwin et al. WO2003044079 describe spin-on-glass anti-reflective coatings for photolithography, noting that organic anti-reflective coatings (ARCS) share many chemical properties with organic photoresist that limit useable process sequences in that that ARCs may intermix with photoresist layers Baldwin et al. propose one solution to avoid intermixing by introducing thermosetting binders as additional components of ARCs. These consist of the binders taught by Flaim et al., U.S. Pat. No. 5,693,691.
Okeda et al. et al., United States Patent Publication No. 20070146887, paragraphs [0309], [0549], [0557], and [0688] to [0716] describe various mixtures of compounds and compositions in antireflection films used in the manufacture of liquid crystal displays.